Me and my Geeky Hobbies

Solderability of Enamelled Copper Wire

Kevin asked about the solderability of the wire I had used in the wiring pencil. I picked the wire I had in stock that was subjectively the was the right gauge and the easiest to solder based on past experience. I hadn't however made detailed tests, so this quick experiment was undertaken to detail the performance of the particular brands I had in stock.

I just happen to have a wide variety of gauges and brands of wire in stock, collected over the years from various suppliers. The supplies may no longer carry the particular wire I tested, or carry something different identified by the same catalogue number, so this data is only really for my benefit, but the experiment is easy to perform for yourself.

I generally find enamelled copper wire is much easier to tin from a cut end. Submerging the cut end in a puddle of solder on the tip of the iron will rapidly burn back the varnish except for especially refractory varnishes, of which I only have a few samples, mostly on quite heavy gauge wire. Tinning in the middle of an unbroken length is generally quite difficult, at normal soldering temperature, except for very fine gauge wires.

I have a cheap DSE sourced temperature controlled soldering station (catalogue number T-1976) which I purchased last year after my previous unit (also DSE sourced, the more expensive T-2200) was no longer supported by DSE for spares and I was in need of a new element. The unit is adjustable from 250 - 450 °C. I normally run at 340 °C, so I picked four test temperatures, starting with 340 °C and going right up the the units limit of 450 °C. Temperatures below 340 °C were not investigated.

Samples of wire were taped to a cardboard frame and tinning attempted at each of the four temperatures. The heat effected zones may have overlapped, especially for the thicker more conductive gauges, but lower temperatures were attempted first, progressing to higher ones. The tinning was attempted to a maximum of 20 seconds per test. Wires up to 500 um only were tested.

This is a twisted pair of red and green wires, intended for easy construction of bifilar RF transformers. Both colours behave the same. Tins with rubbing eventually, but not at the lowest temperature. Higher temperatures tin easier. Somewhat difficult to tin from a cut end at the lowest temperature. No burnt material at high temperatures, but the enamel colour fades in the heat effected region, appears to thin out and melt away from the heat.

Unknown

NA

400 um

Dark Amber

No

No

OK

OK

Sourced from Wyong Field Day 2009. Needs lots of neat to tin. Was the only material that didn't tin eventually at 380 °C.

Unknown

NA

250 um

Light Amber

No

OK

OK

Poor

Sourced from Wyong Field Day 2009. Fairly typical of the harder to tin wires. Burnt material at high temperatures.

In general the results indicate thinner gauges are easier to tin. All wires tested tin from a cut end at the lowest temperature, but may take quite some time and effort/rubbing. All wires will tin mid-wire eventually at 380 °C, but some can take quite a long time and require rubbing back and forth with the iron to start penetration of the enamel. At 410 °C and above all wires tin pretty easily. Higher temperatures are more robust and quicker to tin, but also tend to produce more blackening and slaggy solder.

Wires that tin only with difficulty tend to produce a blackened region near the edge of the enamel layer which appears to be a mixture of burnt enamel and rosin flux. The blackening also seems correlated with decreasing quality of the solder. Wire that really needed a lot of cooking produces very slaggy solder that ideally would be removed and replaced with fresh material to make a nice joint.

The smell of the hardier enamel burning is quite different to that of the easily tinned material. There is a fair variety of enamel chemistries available, but I am unsure which correspond to the easiest tinning wires as the wire is uncharacterised as to its particular enamel chemistry. At least here in Australia, unless you order directly from a wire supplier, you seem to get almost random material. In particular the same type of spools are used for different kinds of wire, probably because of rebranding and splitting of bulk lots by the retailers. Some material purchased years apart, but of the same gauge, colour and brand has different enamel. This will no doubt frustrate attempts to use the data above.

One thing I didn't test which might be of more practical value is tinning when twisted around an IC socket pin in contact with PCB pads. This is the ultimate fate of the wire used in the wiring pencil, so good performance there is highly desirable. The two easiest to tin materials also happen to be those I chose for the wiring pencil, and I know that in practice they work quite well in that application. Unfortunately they are also the oldest sourced and perhaps are no longer consistent with what is currently offered by Dick Smith.